Failures in regulator valves or gas governors can be diagnosed by detecting the occurrence of stick-slip in a contact sliding portion. Stick-slip occurs due to the state of a piston 101, a cylinder 102, and a contact sliding portion 103, as illustrated in, for example, FIG. 8. For example, this stick-slip occurs when, for example, contamination incurs into the contact sliding portion 103. Consequently, stick-slip can be detected by detecting the state of a measured dislocation by detecting the dislocation of the piston 101. (See Japanese Patent 3254624 (“JP '624”).)
Here a simple explanation will be given regarding the detection of stick-slip set forth in JP '624. In this detecting technique, the dislocation of the piston 101 is detected, a first state quantity is calculated from the detected dislocation, a second state quantity is calculated from the detected dislocation, and a ratio of the first state quantity and the second state quantity obtained from the dislocation during proper operation is compared to a ratio of the calculated first state quantity and second state quantity, to detect (evaluate) the stick-slip. In this detection of stick-slip, the ratio of the first state quantity and the second state quantity may be termed a “stick-slip indicator.”
For example, the average of the absolute values of first-order difference values for the dislocation may be used as the first state quantity, and the root mean square of the first-order difference values of the dislocation may be used as the second state quantity. When the dislocations of the piston 101 are detected discreetly and the ith detected dislocation is defined as Xi, then the respective state quantities can be expressed using Expression (1) and Expression (2), below (wherein N is the number of dislocation data used for calculating the state quantities):
                    [                  Expressions          ⁢                                          ⁢          1          ⁢                                          ⁢          and          ⁢                                          ⁢          2                ]                                                                      (                      First            ⁢                                                  ⁢            State            ⁢                                                  ⁢            Quantity                    )                =                              1                          N              -              1                                ⁢                                    ∑                              i                =                1                                            N                -                1                                      ⁢                                                  ⁢                                                                          X                                      i                    +                    1                                                  -                                  X                  i                                                                                                      (        1        )                                          (                      Second            ⁢                                                  ⁢            State            ⁢                                                  ⁢            Quantity                    )                =                                            1                              N                -                1                                      ⁢                                          ∑                                  i                  =                  1                                                  N                  -                  1                                            ⁢                                                          ⁢                                                (                                                            X                                              i                        +                        1                                                              -                                          X                      i                                                        )                                2                                                                        (        2        )            
The frequency distribution of the absolute values (|Xi+1-Xi|) of the first-order differences of the dislocation is as illustrated in FIG. 9 and FIG. 10. FIG. 9 illustrates the state during proper operation, wherein the frequency of occurrence falls smoothly with increasing magnitude of the difference values. On the other hand, if stick-slip occurs, then a majority of the time will be a stationary state, and then slipping will occur occasionally. Because of this, the frequencies of the first-order difference values will have high frequencies clustered around zero, as illustrated in FIG. 10, (corresponding to the stationary state), with relatively large values at low frequencies (corresponding to the slipping state). In the state wherein this type of stick-slip occurs, the ratio of the first state quantity (the average value of the absolute values of the first-order difference values) to the second state quantity (the root mean square of the first-order difference values) will be larger than during proper operation, making it possible to detect the occurrence of stick-slip by monitoring the two state quantities.
In the technology disclosed in JP '624, the detection is performed through the relationship of two state quantities calculated, from the dislocation of a moving portion, by calculating the motion that is subject to stick-slip detection, divided into a stationary state and a slipping state. This makes the determination using only the dislocation of the moving portion. Because of this, if the movement (dislocation) of the moving portion is similar to that of the stick-slip state, then an incorrect evaluation will be that there is stick-slip, even if the stick-slip has not actually occurred. This shall be termed “false stick-slip detection.”
For example, in the control of a valve stem position in a regulator valve using a positioner, if there is a large change in the valve stem dislocation control instruction value (a setting opening), then the behavior of the dislocation of the valve stem (the moving portion) at the time of the change of the control instruction value may be similar to that of the stick-slip state.
As illustrated in FIG. 11 (a), when control instruction values for dislocations wherein the time-series signals form a square wave by alternating two values over time, then the response of the valve stem dislocation for the regulator valve can, accordingly, be measured as the dislocation measurement values for the time-series signals as illustrated in FIG. 11 (b). The first-order difference values in this type of dislocation measurement value can be as illustrated in FIG. 11 (c). In this case, as illustrated in FIG. 11 (c), the majority of the first-order difference values can be clustered near to zero, where only the values immediately after the control instruction value has changed will be large.
This behavior is identical to the behavior of the stick-slip phenomenon wherein there is a stationary state the majority of the time, with occasional rapid movement in the slipping state. The result is that, in the technology of JP '624, there can be false detection of the occurrence of stick-slip when control is performed as illustrated in FIG. 11 (a). This false detection tends to occur when the operating speed of the valve is high, and is particularly problematic in small valves.
Given this, the present applicant has proposed, as a method for controlling false detection of stick-slip, the technology disclosed in Japanese Unexamined Patent Application Publication 2011-80787 (“JP '787”). In the technology disclosed in JP '787 not only is a stick-slip indicator calculated from the dislocations, but from the control instruction values as well, where the stick-slip indicator that is calculated from the dislocations is defined as a first stick-slip indicator and the stick-slip indicator that is calculated from the control instruction values is defined as a second stick-slip indicator, where if the second stick-slip indicator is greater than the first stick-slip indicator, then the stick-slip detection is not applicable.
That is, when a control instruction value is applied that causes an operation wherein it is concluded that a stick-slip has occurred, the dislocation of a movable portion that is operating properly behaves more smoothly than the control instruction value. In this case, the second stick-slip indicator, which is calculated from the control instruction values, is larger than the first stick-slip indicator, which is calculated from the dislocations of the sliding portion. Consequently, it is possible to prevent false detection of stick-slip by omitting from applicability of stick-slip detection those cases wherein the second stick-slip indicator is greater than the first stick-slip indicator.
However, the technology disclosed in JP '787 cannot be said to be perfect, and cannot be said to be able to prevent, with high accuracy, false detection of stick-slip.
FIGS. 12 (a) and (b) show a comparison of changes in control instruction values when it has been possible to control false detection of the stick-slip versus changes in control instruction values when it has not been possible. In both FIGS. 12 (a) and (b), actually the states are when stick-slip has not occurred, where FIG. 12 (a) is an example of having been able to control false detection of stick-slip and FIG. 12 (b) is an example wherein it has not been possible to control false detection of stick-slip.
In these examples, SSpv is the first stick-slip indicator, calculated from the dislocation, SSsp is the second stick-slip indicator, calculated from the control instruction values, and Th is a threshold value for evaluating proper operation/faulty for the first stick-slip indicator SSpv. Note that in this example, the threshold value Th is established as Th=10.
In both FIGS. 12 (a) and (b), the movement of the valve repeats between “stopped” and “rapid change in opening,” such as in stick-slip, where, in FIG. 12 (a) the calculations are SSpv=16.00 and SSsp=16.97, and in FIG. 12 (b) the calculations are SSpv=10.32, and SSsp=10.26.
In FIG. 12 (a) SSpv is 16.00, and because this is greater than the threshold value Th=10 (SSpv>Th), then, by the technology disclosed in JP '624, this would be detected as an occurrence of stick-slip. However, SSsp is 16.97, which is equal to or greater than SSpv=16.00 (SSsp≧SSpv). Because of this, by the technology disclosed in JP '787, this is excluded from applicability of stick-slip detection. Consequently, false detection of stick-slip is prevented in the example illustrated in FIG. 12 (a).
In FIG. 12 (b) SSpv is 10.32, and because this is greater than the threshold value Th=10 (SSpv>Th), then, by the technology disclosed in JP '624, this would be detected as an occurrence of stick-slip. In this case, SSsp is 10.26, which is less than SSpv=10.32 (SSsp<SSpv). Because of this, by the technology disclosed in JP '787, this is not excluded from applicability of stick-slip detection. Consequently, false detection of stick-slip occurs in the example illustrated in FIG. 12 (b).
In this way, in the technology disclosed in JP '787 false detection of stick-slip will occur on occasion, and thus it cannot be said that false detection of stick-slip is prevented with high accuracy.
The present invention was created in order to solve such problems, and the object thereof is to provide a stick-slip detecting device and detecting method able to prevent, with high accuracy, false detection of stick-slip.